Controlled caving for solution mining methods



Jan. 5, 1960 9 K. c. RULE 2,919,909

CONTROLLED CAVING FOR SOLUTION MINING METHODS Filed March 27, 1958 2 Sheets-Sheet 1 TIaJ INVE TOR HP 3.7. n R l/ Jan. 5, 1960 K. c. RULE 2,919,909

CONTROLLED CAVING FOR SOLUTION MINING METHODS Filed March 27, 1958 2 Sheets-Sheet 2 INVENTOR CONTROLLED CAVING FOR SOLUTION I MINING METHODS Kenneth C. Rule, Noroton Heights, Conn., assignor to Food Machinery and Chemical Corporation, New York, N.Y., a corporation of Delaware Application March 27, 1958, Serial No. 724,401,17 11 Claims. (Cl. 262 -3) to the mining of other soluble and liquifiable. under-.

ground mineral formations. V

In the vicinity of Green River, Wyoming, large beds of trona have been found at a depth of. about 1500 feet.

underground. The lowermost trona bed or layer is approximately 12 feet in thickness and overlying the main trona bed are alternate layers of shale and thinner trona layers extending upwardly to approximatelyv 1200 feet below the ground surface. Including the main trona bed and the overlying thinner layers the total trona in the deposit is over 40 feet in thickness.

In the solution mining of trona from this formation it is the present practice to connect .two spaced wells through the lower trona bed by hydraulically fracturing the formation substantially at the interface of the lower trona bed and the underlying shale formation and to start solution mining from the bottom of the lower bed by circulating a dissolving liquid through the fracture to dissolve the trona in the lower bed, beginning from the bottom upwardly.

It is an object of this invention to improve the recovery of trona from this formation by systematically exposing the trona in the upper trona beds to the action of the dissolving liquid.

Another object of this invention is to provide a method for recovering trona from the upper trona beds by solution mining.

Another object of the invention is to provide a method of controlled caving of the upper trona beds after a portion of the lower trona bed has been removed by solution mining whereby circulation of the underground solution can be directed in such a Way as to dissolve out more of the trona from the lower trona bed and to prevent short *circuiting of the solution between the wells.

Another object of the invention is to expose more of the trona bed to solution mining where portions of the trona bed have been bypassed by the flow of the mining solution therethrough.

These same objects are applicable to the solution mining of other salt and similar deposits which can be removed in liquified form from underground formations.

Various other objects and advantages of the invention will appear as this description proceeds.

Referring now to the drawings:

Fig, l is a diagrammatic illustration of a trona deposit in which solution mining in the lower bed has already taken place.

--Fig. 2 is a plan view illustrating how controlled eav- United States Patent ing by the method herein described can be used todissolve more trona from the formation.

Fig. 3 is a plan view of an illustrative solution miningf layout showing how this invention may be applied thereto..

As illustrated in Fig. l, the maintrona bed consists of a layer 10 approximately 12 feet in thickness and ap-.

proximately 1500 feet underground. Below the trona bed is a layer of shale 11 and above the trona bed is anhas been established by hydraulically fracturing theffo rmotion between these wells by introducing a hydraulic. fluid into the formation under sufficient pressure ,to. cause parting of the formation starting substantially atthe interface between the lower trona bed andthe underlying shale layer as described, for example, inpatent applica-.

tion Serial No. 564,417, filed February 9, 1956, now.

Patent No. 2,847,202. A dissolving solution is thencirculated between well'A and well B to dissolve out the: trona between wells A and B in the lower trona bed 10 forming what is believed to be a roughly elliptical shaped cavity 12 between the wells A and B as illustrated in Fig. 2. Wells A and B may, for example, be of the order.

of 600 to 2000 feet apart.

Due to the somewhat impervious and insoluble nature of the shale layers 11 and 11a substantially no shale is dissolved or removed from these layers and the tendency. is to dissolve trona only from the lower trona bed in the path of circulation between the wells A and B. Due to the hydrostatic pressure of the solution head against theunderside of the shale layer 11a the roof of the solution cavity is supported and the tendency of the shale. layer 11a to cave is materially reduced.

While some insoluble material contained in the trona and flaking from the shale is deposited in the bottom of.

the cavity 12 as indicated at 13, the cavitytends to en-- large by dissolving trona around the periphery of the cavityand due to the upward pressure of the dissolvingsolution Within the cavity on the shale layer 11a caving;

from the roof does not take place to any material extent and the solution largely is confined within the lower trona bed 10. It is undesirable to have caving adjacent wells- A and B because this sometimes causes bending of the well casings, which interferes with cleaning and other operations, and severe caving adjacent well-s A or B- might result in plugging these wells and stoppage of flow of solution fluid therethrough. I

In'accordance with the practice of this invention controlled caving may be induced between wells A and B by drilling a well C into the formation and into one of the upper trona beds. The well C is then underreamed at 'C, cased and cemented according to the usual practice and a hydraulic fracturing pressure is applied to the underreamed portion by pumping a suitable hydraulic fluid under pressure through the casing of well C and into the underrearned section C until the fracturing'pressure is exceeded. a

7 Due to the fact that the overburden extends for several hundred feet above the bottom of the well C to the ground surface and that the depth of the trona formation below the bottom of well C extending downward to the solution mined cavity 12 may be of any desired distance from, for example, 25 to 200 feet depending upon the depth of well C, the application of the hydraulic fracturing pressure through the well C tends to develop hori' zontally along the interface between the trona bed 1019 into which the well C extends and the adjacent shale layer 11b until-suflicient pressure-has been -applied to Patented Jan, 5 196,0.

overcome the resistance to caving after which a large area, such as indicated in dotted lines 15, will be caused to cave and drop into the already solution mined area 12 and assume a position somewhat as indicated at 15a.

Referring to Fig. 2 the outline of the caved deposit is indicated at 15a. By caving the upper layer in this manner the upper trona layers 1% are exposed at their edges, a large amount of dissolvable trona is deposited in the caved material 15a in the cavity 12 already out between the wells A and B and the path of the mining liquid is now directed in two flows indicated by the arrows 16a and 1512 around the caved portion 15a from the well A to the well B thereby bringing more of the trona in the bed into contact with the solution mining liquid, while at the same time the trona in the caved portion a is dissolved by the percolation of the dissolving liquid therethrough. Any tendency of the solution liquid to short circuit be tween wells A and B is reduced by the caved portion 15a.

While it is preferred to induce the caving by the use of gradually applied hydraulic fracturing pressure, it will be understood, of course, that substantially the same results can be secured by inserting an explosive charge at the bottom of well C and exploding the charge according to oil well shooting practice. This, however, does not produce as uniform an area of caving as the use of a hydraulic fracturing pressure at the bottom of well C and is more likely to cause damage to the casings of wells A and B. During the hydraulic fracturing operation at the bottom of well C it is desirable to relieve the upward pressure of the solution in the cavity 12 against the under portion of the shale layer 3.1a as much as possible by discontinuing the pumping of solution fluid under pressure into wells A and B and opening these well heads to atmospheric pressure or by pumping out a portion of the fluid in the upper parts of wells A and B to relieve the hydrostatic pressure head on the formation.

Fig. 3 shows a diagrammatic pattern for solution mining in which after forming cavity 12 around wells A and B, well D is connected to well B by hydraulic fracturing and a cavity 12a is formed by circulation of a dissolving fluid between these wells. In a similar manner cavities 12b and 120 are formed between wells E and D and wells E and A leaving a substantial unmined portion between the cavities 12, 12a, 12b and 120. In this arrangement controlled caving can be induced from wells C C C and C As indicated at C and C this caving may be along the outer edges of cavities 12a and 120 to cause solution mining fluid to be directed against the unmined portion or pillar 20 by the caved deposits 15:: to facilitate dissolving out this pillar.

After the caving, Wells C may be used for the introduction or withdrawal of solution mining liquid to thereby create new flow patterns between the wells and expose more trona to contact with the dissolving liquid. If desired, the wells C, C C C and C may be of considerably smaller diameter than the producing wells A and B, thereby reducing the cost thereof.

Caving of the area indicated at 15 leaves the edges of the alternate trona layers 1% and shale layers 11b exposed to contact with the dissolving liquid. In subsequent solution mining of the cavity exposed by caving area 15 the mining solution will penetrate and dissolve trona from the exposed edges of layers 1012. This will result in the removal of support for the shale layers 11b and the edges of these layers wil gradually cave into the cavity 12. This caving will, however, be a gradual caving removed from the immediate vicinity of wells A and B so that danger of bending or plugging the casings of these wells is reduced. This process will continue to dissolve and expose larger areas around the cavity 15 and will ultimately lead to the solution and removal of substantially all of the trona in layers in!) between wells A and B without, however, exposing these wells to large uncontrolled caving immediately adjacent these wells.

If wells C are not to be used for the introduction or removal of solution mining liquor the casing and cementing of the walls C may be omitted and the caving induced therefrom by inserting a packer at the bottom of the well and above the underreamed section C to confine the hydraulic fracturing fluid at the desired level, and the hydraulic fracturing fluid may be introduced through tubing communicating with the packer. As indicated above, an explosive charge may be exploded at the bottom of wells C to cause caving but this is not the preferred procedure.

In the event that well C is inadvertently drilled into the solution mined cavity 12 it may be plugged at the desired distance above the cavity 12 by inserting a suitable packer and the hydraulic fracturing pressure may be applied to the formation above the packers. The well C, if desired, may be underreamed above the packer in this instance.

After the initial caving from the bottom of well C additional caving can be produced above the bottom of well C by inserting a packer at the point where the additional caving is desired, perforating the casing of well C above the packer and pumping a fracturing fluid into the formation under sufficient pressure to produce the desired caving. This process can be repeated at spaced intervals along the well C until all the layers of trona above the cavity 12 and adjacent the well C have been caved into the solution mined cavity. If the well C is not cased the same results may be secured by inserting packers at successively higher levels in the well and applying fracturing pressure above the packers.

While the application of the invention has been de scribed with specific reference to inducing caving from above into a solution mined cavity in a multiple layered trona deposit it will be understood that the invention is applicable to solution mined sodium chloride and other salt deposits and also to sulfur and other deposits removable in liquid form from an underground formation as well as to other underground cavities into which it is desired to produce controlled caving. Where a homogeneous salt layer several hundred feet in thickness is being mined it is possible to induce controlled caving from the upper salt bed into a solution mined cavity by the use of the method described.

Other methods of applying controlled caving to a solution mined field will be readily apparent to persons skilled in the art in view of the above illustrative description.

While the invention has been described with particular reference to the solution mining of trona located in spaced horizontal beds, such as in the Green River, Wyoming formation, it will be understood that the invention is also applicable to other salt and liquid mining methods, such as the mining of sulfur, and that various modifications and changes can be made in the method described without departing from the spirit of this invention or the scope of the following claims.

I claim:

1. The method of solution mining which comprises forming a cavity between spaced wells by passing a solvent through a soluble formation between the spaced wells and inducing controlled caving into said cavity between the wells by drilling an intermediate well into the formation, stopping the intermediate well at a substantial distance above the said cavity and inducing caving from the intermediate well by applying a caving pressure adjacent the bottom of the intermediate well to cave a portion of the overlying formation into the cavity produced by the solution mining.

2. The method of claim 1 in which the pressure on the cavity is reduced during the application of the caving pressure.

3. The method of liquid mining which comprises forming a cavity between spaced wells by passing a removal liquid through a formation removable in liquid form between the spaced wells and inducing controlled caving into said cavity between the wells by drilling an inter- 5 mediate Well into the formation, stopping the intermediate well at a substantial distance above the said cavity and inducing caving from the intermediate well by applying a caving pressure adjacent the bottom of the intermediate well to cave a portion of the overlying formation into the cavity produced by the removal liquid.

4. The method of controlling caving in a solution mining operation which comprises passing a removal liquid between two spaced wells in an underground mineral formation removable in liquescent form until a substantial underground cavity has been formed between the two wells and then inducing controlled caving of the formation into the cavity by drilling an intermediate well into the formation, stopping said intermediate well at a vertically spaced distance above the said cavity and causing caving into said cavity from the bottom of the intermediate well by applying a hydraulic fracturing pressure adjacent the bottom of the intermediate well to cave a portion of the formation into the solution mined cavity.

5. The method of controlling caving in a solution mining operation which comprises passing a removal liquid between two spaced wells in an underground mineral formation removable in liquescent form until a substantial underground cavity has been formed between the two wells and then inducing controlled caving of the formation into the cavity by drilling an intermediate well into the formation, stopping said intermediate well at a distance above the said cavity, underreaming the intermediate well at the bottom and causing caving into said cavity from the bottom of the intermediate well by applying a hydraulic fracturing pressure at the bottom of the intermediate well to cave a portion of the overlying formation into the solution mined cavity.

6. The method of solution mining of trona in a plurality of underground layers interspersed with layers of shale which comprises drilling spaced wells into the lower layer of said trona formation, hydraulically fracturing said trona layer at the lower interface to produce communication between said wells, circulating a dissolving liquid between said wells to dissolve trona from said lower trona layer and form a cavity therein drilling an intermediate well into the formation, stopping the intermediate well at a substantial distance above said cavity and inducing controlled caving from said intermediate well into said cavity between said wells to expose trona in the upper layers of said formation to said dissolving liquid by applying a caving pressure adjacent the bottom of said intermediate well.

7. The method of solution mining of trona in a plurality of underground layers interspersed with layers of shale which comprises drilling spaced wells into the lower layer of said trona formation, hydraulically fracturing said trona layer at the lower interface to produce communication between said wells, circulating a dissolving liquid between said wells to dissolve trona from said lower trona layer and form a cavity therein, drilling an intermediate well into an upper trona layer in said formation, stopping the intermediate well at a substantial distance above said cavity and inducing controlled caving from said intermediate well into said cavity between said wells to expose trona in the upper layers of said formation to said dissolving liquid by applying a caving pressure adjacent the bottom of said intermediate well.

8. The method of solution mining of trona lying in a plurality of underground layers separated by layers of shale which comprises drilling spaced wells into the trona formation substantially to the bottom of the lower trona layer, hydraulically fracturing the formation between said wells to produce underground communication between said wells, circulating a dissolving liquid between said wells to dissolve trona from said lower trona layer and form a cavity therein and exposing upper layers of trona to solution mining by drilling an intermediate well into the formation, stopping the intermediate well at a substantial distance above said cavity and inducing controlled caving into said cavity from said intermediate well to cave upper'layers of trona and shale into said cavity by applying a caving pressure adjacent the bottom of said intermediate well, and circulating a dissolving liquid around said caved section and through said caved area to dissolve more trona therefrom.

9. The method of solution mining of trona lying in a plurality of underground layers separated by layers of shale which comprism drilling spaced wells into the trona formation substantially to the bottom of the lower trona layer, hydraulically fracturing the formation between said wells to produce underground communication between said wells, circulating a dissolving liquid between said wells to dissolve trona from said lower trona layer and form a cavity therein and exposing upper layers of trona to solution mining by drilling an intermediate well into the trona formation to an upper trona layer therein, stopping the intermediate well at a substantial distance above said cavity and causing caving of the upper layers of trona and shale into said cavity from the bottom of said intermediate well by applying a caving pressure adjacent the bottom of said intermediate well, and circulating a dissolving liquid around said caved section and through said caved area to dissolve more trona therefrom.

10. The method of solution mining of trona lying in a plurality of underground layers separated by layers of shale which comprises drilling spaced wells into the trona formation substantially to the bottom of the lower trona layer, hydraulically fracturing the formation between said wells to produce underground communication between said wells, circulating a dissolving liquid between said wells to dissolve trona from said lower trona layer and form a cavity in the formation and exposing upper layers of trona to solution mining by drilling an intermediate well into the trona formation to an upper trona layer therein, stopping the intermediate well at a substantial distance above said cavity, hydraulically fracturing the formation adjacent the intermediate well and caving a portion of the upper layers of trona and shale into said cavity from the bottom of said intermediate well, and circulating a dissolving liquid around said caved section and through said caved area to dissolve more trona therefrom.

11. The method of producing controlled caving into an underground mining cavity which comprises forming an underground mining cavity in the formation, drilling a well into the formation above said cavity, stopping the well at a substantial distance above said cavity and inducing caving from substantially the bottom of said well by applying a caving pressure adjacent the bottom of said well to cave a portion of the overlying formation into said cavity.

References Cited in the file of this patent UNITED STATES PATENTS 

